A facility for three-demensional computer reconstruction of subcellular structure is proposed. Thick (about .2-.5Mu) sections containing the biological structure are imaged using the Albany high-voltage electron microscope (HVEM) Biotechnology facility. Projections are obtained in a wide range of angles. Construction of a eucentric double tilt goniometer stage is proposed to replace the existing stage. The micrographs of tilt series are digitized, and the three-dimensional reconstruction is performed with a dedicated computer using the modified back projection algorithm. Windowing of the data, intermediate results and final reconstruction are viewed on a computer-linked high-speed graphics terminal. The facility will be used to study the detailed morphology of microtubular organizing centers and the three-dimensional organization of microtubules in reticulopods. A modular, user-friendly software system for image processing and three-dimensional reconstruction already exists. The general feasibility of this approach to subcellular structure visualization with the HVEM will be explored. The configuration and organization of a National resource facility allowing reconstruction from projections of thick sections will be defined, in terms of additional equipment needs and staffing.